Turbomachines are widely utilized in fields such as power generation. For example, a conventional gas turbine system includes a compressor section, a combustor section, and at least one turbine section. The compressor section is configured to compress air as the air flows through the compressor section. The air is then flowed from the compressor section to the combustor section, where it is mixed with fuel and combusted, generating a hot gas flow. The hot gas flow is provided to the turbine section, which utilizes the hot gas flow by extracting energy from it to power the compressor, an electrical generator, and other various loads.
A typical compressor for a gas turbine may be configured as a multi-stage axial compressor and may include both rotating and stationary components. A shaft drives a central rotor drum or wheel, which has a number of annular rotors. Rotor stages of the compressor rotate between a similar number of stationary stator stages, with each rotor stage including a plurality of rotor blades secured to the rotor wheel and each stator stage including a plurality of stator vanes secured to an outer casing of the compressor. During operation, airflow passes through the compressor stages and is sequentially compressed, with each succeeding downstream stage increasing the pressure until the air is discharged from the compressor outlet at a maximum pressure.
In order to improve the performance of a compressor, one or more of the stator stages may include variable stator vanes, or variable vanes, configured to be rotated about their longitudinal or radial axes. Such variable stator vanes generally permit compressor efficiency and operability to be enhanced by controlling the amount of air flowing into and through the compressor by varying the angle at which the stator vanes are oriented relative to the flow of air.
In particular gas turbines, the compressor section may include a row of inlet guide vanes disposed generally adjacent to an inlet of the compressor section. In addition or in the alternative, the compressor section may include a row of variable stator vanes downstream from the inlet guide vanes. In certain gas turbine designs, the compressor section may include multiple rows of the variable stator vanes. Typically, a row of rotor blades is disposed between the inlet guide vanes and the variable stator vanes. During various operating conditions, such as startup and shut down of the gas turbine, the inlet guide vanes and the variable stator vanes may be actuated between an open position and a closed position so as to increase or decrease a flow rate of the working fluid entering the compressor section of the gas turbine.
When the gas turbine enters an operating condition known in the industry as “part-load operation,” the inlet guide vanes and the variable stator vanes are actuated to the closed position or a partially closed condition to reduce or minimize airflow through the gas turbine. This may improve the efficiency of the compressor when the gas turbine is operating in a part-load condition. However, this doesn't optimize the flow condition over the full radial dimension of the vane, in particular for vanes with a large radial dimension. This results in non-optimal, disturbed flow condition either at the vane tip or the vane hub. Due to the different flow conditions at different radial coordinates, a solid vane with a fixed incidence angle cannot always function optimally under a range of operating load conditions, e.g., baseload and part-load. Usually a vane is designed for a designated operation range, e.g., baseload, which may be less efficient at other operating conditions, such as part-load operations.